Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Directional couplers are provided. In one embodiment, the directional
coupler includes first and second transmission line segments positioned
on a first plane and spaced apart by a first distance, third and fourth
transmission line segments positioned on a second plane and spaced apart
by a second distance, the second plane spaced apart from the first plane,
a first conductive segment connecting the first and third transmission
line segments, and a second conductive segment connecting the second and
fourth transmission line segments, where the first and second
transmission line segments are configured to couple energy therebetween,
and where the third and fourth transmission line segments are configured
to couple energy therebetween.

Claims:

1. A directional coupler comprising: first and second transmission line
segments positioned on a first plane and spaced apart by a first
distance; third and fourth transmission line segments positioned on a
second plane and spaced apart by a second distance, the second plane
spaced apart from the first plane; a first conductive segment connecting
the first and third transmission line segments; and a second conductive
segment connecting the second and fourth transmission line segments,
wherein the first and second transmission line segments are configured to
couple energy therebetween, and wherein the third and fourth transmission
line segments are configured to couple energy therebetween.

2. The coupler of claim 1: wherein an amount of energy coupled between
the first and second transmission line segments is determined, at least
in part, by the first distance; and wherein an amount of energy coupled
between the third and fourth transmission line segments is determined, at
least in part, by the second distance.

3. The coupler of claim 1: wherein the first transmission line segment,
the third transmission line segment, and the first conductive segment
comprise an I-beam shaped cross section; and wherein the second
transmission line segment, the fourth transmission line segment, and the
second conductive segment comprise an I-beam shaped cross section.

4. The coupler of claim 1: wherein the first transmission line segment,
the third transmission line segment, and the first conductive segment
comprise an J-shaped cross section; and wherein the second transmission
line segment, the fourth transmission line segment, and the second
conductive segment comprise an J-shaped cross section.

5. The coupler of claim 1: wherein the first and second transmission line
segments comprise a conductor having a rectangular cross section and an
elongated length; wherein the third and fourth transmission line segments
comprise a conductor having a rectangular cross section and an elongated
length; and wherein the first and second conductive segments comprise a
conductor having a rectangular cross section and an elongated length.

6. The coupler of claim 5: wherein a length of each of the rectangular
cross sections of the first, second, third, and fourth transmission line
segments extends in a first direction; wherein a length of each of the
rectangular cross sections of the first and second conductive segments
extends in a second direction transverse to the first direction.

7. The coupler of claim 5: wherein the elongated lengths of the first and
second conductive segments comprise periodic gaps.

8. The coupler of claim 1, further comprising: fifth and sixth
transmission line segments positioned on a third plane and spaced apart
by a third distance, the third plane spaced apart from the first and
second planes; and a third conductive segment connecting the fifth and
sixth transmission line segments; and wherein the fifth and sixth
transmission line segments are configured to couple energy therebetween.

9. The coupler of claim 1, wherein the first, second, third, and fourth
transmission line segments comprise at least one conductive material.

10. The coupler of claim 9: wherein the at least conductive material
comprises copper, and wherein the first and second conductive segments
comprise tungsten.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates generally to directional couplers.
More specifically, the invention relates to a microwave directional
coupler having a structure that allows for coupling along more than one
plane.

BACKGROUND

[0002] Directional couplers are passive devices typically used in radio
frequency applications to couple part of the transmission power or energy
in a transmission line by a known amount out through another port. Often
the coupling is achieved by using two transmission lines set close enough
together such that energy passing through one line is coupled to the
other line. Designers of directional couplers often need to determine a
mechanical layout of these transmission lines to accomplish a preselected
degree of coupling. Often this preselected degree of coupling is 3 dB or
less and constrains the designer to position the lines very close
together, which can create manufacturing and/or fabrication yield
problems. More specifically, in some cases, the designer can be
constrained by the rules associated with a design tool for laying out the
transmission lines.

[0003] Conventional directional couplers can include interdigitated
coupling segments positioned on a flat surface. U.S. Pat. No. 3,516,024
to Lange describes such an interdigitated strip line coupler. A variation
of the Lange coupler is described by Waugh and LaCombe in an IEEE
article. (Waugh, R., LaCombe, D.: "`Unfolding` the Lange Coupler", IEEE
Trans., 1972, MTT-20, pp. 777-779). These conventional couplers can
however be difficult and expensive to manufacture in some circumstances.
In addition, the performance of these conventional couplers can be
limited.

SUMMARY

[0004] Aspects of the invention relate to directional couplers that allow
for coupling on more than one plane. In one embodiment, the directional
coupler includes first and second transmission line segments positioned
on a first plane and spaced apart by a first distance, third and fourth
transmission line segments positioned on a second plane and spaced apart
by a second distance, the second plane spaced apart from the first plane,
a first conductive segment connecting the first and third transmission
line segments, and a second conductive segment connecting the second and
fourth transmission line segments, where the first and second
transmission line segments are configured to couple energy therebetween,
and where the third and fourth transmission line segments are configured
to couple energy therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a top view of a directional coupler in accordance with
one embodiment of the invention.

[0006] FIG. 2 is a perspective view of a portion of the directional
coupler of FIG. 1 in accordance with one embodiment of the invention.

[0007] FIG. 3 is a expanded view of an end portion of the directional
coupler of FIG. 2 in accordance with one embodiment of the invention.

[0008] FIG. 4 is a cross sectional view of a cross section taken along the
transmission line coupling segments of the directional coupler of FIG. 3
in accordance with one embodiment of the invention.

[0009] FIG. 5 is a graph of coupling verses the frequency for a
directional coupler in accordance with one embodiment of the invention.

[0010] FIG. 6 is a graph of relative phase verses the frequency for a
directional coupler in accordance with one embodiment of the invention.

[0011] FIG. 7 is a graph of return loss verses the frequency for a
directional coupler in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

[0012] Referring now to the drawings, embodiments of directional couplers
have a three dimensional structure that provides coupling on more than
one plane. Embodiments of the coupler structures include first and second
transmission line coupling segments positioned on a first plane, spaced
apart by a first distance, and third and fourth transmission line
coupling segments positioned on a second plane, spaced apart by a second
distance, where the second plane is spaced apart from the first plane.
Embodiments of the coupler structures further include conductive segments
that connect the first and third transmission line segments, and the
second and fourth transmission line segments, respectively. The first and
second transmission line segments are configured to couple energy between
the transmission line segments. Similarly, the third and fourth
transmission line segments are configured to couple energy between the
transmission line segments. In contrast to conventional directional
couplers, embodiments of coupler structures described herein provide
coupling on more than one plane using at least two transmission line
coupling segments.

[0013] In some embodiments, a cross section of the coupler structures can
have a I-beam shape. In other embodiments, the coupler structures can
have other suitable shapes.

[0014] FIG. 1 is a top view of a directional coupler in accordance with
one embodiment of the invention. The directional coupler includes a first
transmission line 10 and a second transmission line 12 interleaved among
a number of interconnected ground planes (14, 16, 18, 20). The first and
second transmission lines (10, 12) include closely positioned coupling
segments (10a, 12a) disposed along a first plane that extends in the same
plane as the ground planes (14, 16, 18, 20). The first and second
transmission lines (10, 12) also include closely positioned coupling
segments (see FIG. 2) along a second plane positioned below, or spaced
apart from, the first plane.

[0015] FIG. 2 is a perspective view of a portion of the directional
coupler of FIG. 1 in accordance with one embodiment of the invention.

[0016] FIG. 3 is a expanded view of an end portion of the directional
coupler of FIG. 2 in accordance with one embodiment of the invention.

[0017] FIG. 4 is a cross sectional view of a cross section taken along the
transmission line coupling segments of the directional coupler of FIG. 3
in accordance with one embodiment of the invention.

[0018] Referring now to FIGS. 2-4, the first and second transmission line
coupling segments (10a, 12a) each have an elongated body with a square or
rectangular cross section and are positioned in a top plane. First and
second transverse conductive segments (22, 24) each are attached to a
bottom surface of one of the first and second transmission line segments
(10a, 12a). The transverse conductive segments (22, 24) each have an
elongated body and a rectangular cross section with a length of the cross
section extending perpendicular to the bottom surfaces of each of the
first and second transmission line segments (10a, 12a). Top surfaces of
each of the third and fourth coupling segments (26, 28) are attached to
the transverse conductive segments (22, 24), respectively. The third and
fourth coupling segments (26, 28) each have a rectangular cross section
with a length of the cross section extending perpendicular to the length
of the cross section of the transverse conductive segments (22, 24). The
third and fourth coupling segments (26, 28) are positioned below the
first and second coupling segments (10a, 12a) in a bottom plane spaced
apart from the top plane by a distance about equal to the length of one
of the transverse conductive segments (22, 24). The first and second
coupling segments (10a, 12a) are separated by a top coupling distance or
gap 30, while the third and fourth coupling segments (26, 28) are
separated by a bottom coupling distance or gap 32.

[0019] In the embodiments illustrated in FIGS. 2-4, the first coupling
segment 10a, the first transverse conductive segment 22, and third
coupling segment 26 form an I-beam cross section, or considered from a
different direction, an H-beam cross section. Similarly, the second
coupling segment 12a, the second transverse conductive segment 24, and
fourth coupling segment 28 form an I-beam cross section. For an I-beam
cross section or other similar structure, the coupling segments (10a,
12a, 26, 28) can be referred to as flanges while the transverse
conductive segments (22, 24) can be referred to as webs. The I-beam cross
section with two flanges can provide for better coupling performance than
conventional directional couplers. In particular, as compared to
conventional couplers, the third and fourth coupling segments (26, 28)
can provide coupling in a second plane in addition to the primary
coupling segments (e.g., 10a, 12a).

[0020] The overall degree of coupling is a function of the distances or
gaps (30, 32) between the coupling segments (10a, 12a, 26, 28) or
flanges. More specifically, the smaller the gap (30, 32) between the
flanges, the greater the coupling. The smaller gap can increase the
capacitance between the transmission line (10a to 12a, 22 to 24, and 26
to 28) surfaces facing each other. In the embodiments illustrated in
FIGS. 2-4, the top gap 30 is about equal to the bottom gap 32. In other
embodiments, the gaps can be unequal. In several embodiments, the
distances or gap spacing are determined to achieve a degree of coupling
that is about 3 dB, representing an equal split of the input power level.
In other embodiments, other degrees of coupling can be achieved. In one
embodiment, the top gap is 2.9 microns, and the bottom gap is 2.9
microns. In such case, the first and second conductor widths (10a and
12a) can both be 3.7 microns, while the widths of the third and fourth
transmission line conductors (26 and 28) can also be 3.7 microns. The
widths of the transverse conductive segments (22 and 24) can both be 1.3
microns, the gap between them can be 5.3 microns.

[0021] In several embodiments, the gaps (30, 32) between the flanges are
filled with air. In other embodiments, other dielectric materials can
fill the gaps. In such embodiment, the gaps include various coatings
including 1 um of oxygen, 1.35 um of silicon nitride, 0.45 um of nitride
and an average of 2.5 um of polyimide. In several embodiments, the higher
the dielectric constant of the dielectric material used to fill the gaps,
the greater the gap spacing can be to achieve a preselected degree of
coupling.

[0022] In the embodiments illustrated in FIGS. 2-4, there are two flanges
(10a, 26 and 12a, 28) coupled by a single web (22 and 24) for each
transmission line (10 and 12). In other embodiments, the transmission
line coupling structures may include more than two flanges and additional
webs for additional coupling. In one such case, an additional flange is
positioned on a third plane spaced apart from the top and bottom planes
and coupled to either flange 10a or 26 using an additional web. In FIG.
4, each web is slightly offset from a center of the flanges it is
attached to. More specifically, each web is slightly offset towards the
opposing web. In some embodiments, each web can be positioned even closer
to the opposing web then depicted in FIG. 4. In other embodiments, each
web can be centered with respect to the flanges attached thereto.

[0023] In the embodiment illustrated in FIGS. 2-3, the webs (22, 24)
include periodic gaps 34 along the lengths of the webs. In other
embodiments, these gaps can be wider than illustrated in FIGS. 2-3. In
some embodiments, no gap is present in the webs. In one embodiment, the
gap is due to a design rule associated with a particular software layout
tool. In some embodiments, the gaps has little or no effect on the
coupling performance of the directional coupler. In such case, use of the
gaps serve to minimize cost associated with unnecessary material.

[0024] In the embodiments illustrated in FIGS. 2-4, the directional
coupler includes two coupling structures having an I-beam shaped cross
section. In other embodiments, the coupling structures can have other
suitable cross sectional shapes. In one such embodiment, for example, the
coupling structures can have a J-shaped, T-shaped and/or L-shaped cross
section. In some embodiments, the shape of the coupling structure is
determined, at least in part, based on design rules associated with a
particular software layout tool for transmission lines. In one such
embodiment, those design rules may be provided by a particular foundry
supplying the layout tool. In the embodiments illustrated in FIGS. 2-4,
the directional coupler includes two symmetrical coupling structures. In
other embodiments, the coupling structures are not symmetrical.

[0025] In several embodiments, the coupling structures are made of
conductive materials. In one embodiment, for example, the flanges are
made of copper and the webs are made of tungsten. In other embodiments,
other suitable conductive materials can be used. In some embodiments, the
coupling structures are made of aluminum.

[0026] Returning briefly to FIG. 1, for an electrical performance
analysis, the directional coupler can be considered a four port device
having an input port P1, a transmitted port P2, a coupled port P3, and an
isolated port P4.

[0027] FIG. 5 is a graph of coupling verses the frequency for a
directional coupler in accordance with one embodiment of the invention.
The trace (P3, P1) represents the logarithm of the ratio of the power
into port P3 divided by the power out of the port P1 expressed in
decibels. The trace (P2, P1) represents the degree of coupling appearing
at the transmitted or direct port P2. As illustrated in FIG. 5, the
degree of coupling for the coupled port P3 is at least 3 dB and increases
beyond 4 dB as the frequency increases for the given frequency range.

[0028] FIG. 6 is a graph of relative phase verses the frequency for a
directional coupler in accordance with one embodiment of the invention.
The relative phase can be thought of as the difference in phase between
an input wave to the directional coupler and an output wave of the
directional coupler.

[0029] FIG. 7 is a graph of return loss verses the frequency for each port
of a directional coupler in accordance with one embodiment of the
invention.

[0030] While the above description contains many specific embodiments of
the invention, these should not be construed as limitations on the scope
of the invention, but rather as examples of specific embodiments thereof.
Accordingly, the scope of the invention should be determined not by the
embodiments illustrated, but by the appended claims and their
equivalents.